1. Field of the Invention
The present invention relates to a Fe-based soft magnetic thin film composition, and more particularly, to a FeCoNiN-based soft magnetic thin film composition, which is prepared by addition of nitrogen to a soft magnetic thin film mainly composed of three elements, Fe, Co and Ni using a reactive sputtering to provide excellent high-frequency characteristics in the frequency band of several hundreds of MHz as well as an excellent corrosion resistance characteristic.
2. Description of the Related Art
With the tendency of high frequency and high integration of information and communication equipment, various electronic components concerned have been growingly miniaturized and surface-mounted. However, magnetic heads used in various information recording devices such as computers are much limited in implementation of high performance and high-frequency operations due to the magnetic properties of the soft magnetic material used for a magnetic core. In particular, magnetic devices such as voltage transformer, inductor, or the like for various electronic components are mostly used in the form of a core having a large volume, which is an obstacle to the development of such technologies. It is therefore necessary to develop a soft magnetic thin film material excellent in high-frequency characteristics in order to provide magnetic devices that have a light, thin and simple structure.
Examples of the conventional soft magnetic material include FeAlSi(sendust) alloy, NiFe(permalloy) alloy, and Co-based amorphous alloy. However, these materials have low saturation magnetization and poor high-frequency characteristics, and hence limitations in use for high-frequency thin film magnetic devices. As such, various magnetic thin films have recently been developed based on the Fe-based soft magnetic thin film having ultrafine crystals. These magnetic thin films entirely exhibit high saturation magnetization with poor high-frequency and corrosion characteristics and are disadvantageous in practical uses.
The present inventors have studied on the FeCoNi-based thin film obtained by the sputtering method, which maintains high-frequency characteristics in the frequency band of up to 100 MHz and has a high saturation magnetization and excellent soft magnetic properties. However, this thin film has such a low electrical resistivity and magnetic anisotropy as to abruptly decrease the value of effective permeability in the frequency region of greater than 100 MHz.
It is, therefore, an object of the present invention to solve the problem with the prior art and to provide a novel FeCoNiN-based thin film having an ultrafine crystalline structure obtained by the sputtering method without an additional heat treatment, wherein the thin film maintains a high saturation magnetization of more than 16 kG and has excellent soft magnetic properties at the high frequency band of above 100 MHz as well as a high corrosion resistance.
To achieve the above object of the present invention, there is provided a FeCoNiN-based soft magnetic thin film composition having the formula FexCoyNizNv, wherein x, y, z and v are expressed in at % and satisfy 41xe2x89xa6xxe2x89xa655, 18xe2x89xa6yxe2x89xa627, 19xe2x89xa6zxe2x89xa632, 0 less than vxe2x89xa65, and x+y+z+v=100.
It is undesirable that Fe, Co and Ni contents of the composition are out of the range, because the soft magnetic properties or high-frequency characteristics may deteriorate.
In the present invention, the added amount of nitrogen is limited to 5 at % or less based on the total composition in order to provide an excellent corrosion characteristic and ultrafine crystals of the FeCoNi-based soft magnetic alloy. If the N2 content exceeds the above value, soft magnetic properties such as saturation magnetization and effective permeability are undesirably deteriorated.
The FeCoNiN-based soft magnetic thin film composition of the present invention is prepared by the sputtering method or other physical vapor deposition.
Now, a process for preparing the FeCoNiN-based soft magnetic thin film composition using the sputtering method will be described as follows.
sputtering was performed using the composite target, which consisted of small pieces of Co and Ni, and a Fe disc target. Working pressure was controlled under the gas atmosphere having the nitrogen (N2) content in the sputtering gas (Ar gas) being within 1 to 10% of the total amount of the gas. The thin film obtained was then measured in regard to magnetic properties as well as high-frequency and corrosion resistance characteristics without a separate heat treatment. As a result, it was found that the thin film comprised ultrafine crystals of xcex1-FeCo, NiFe, and xcex1-Co during the deposition process to provide excellent soft magnetic properties. These thin films were much superior in the high-frequency permeability to other soft magnetic thin films having the same grain size, which was because the thin film of the present invention contained N2 as an additive to abruptly increase the electrical resistivity and had a HCP structure of xcex1-Co to increase the magnetic anisotropy energy. The sputtering conditions used in the present invention are presented in Table 1.